The Efficiency of Nitrate Removal in Drinking Water Using Iron Nano-Particle: Determination of Optimum Conditions

Nitrate ion is among the most important pollutants of surface and underground water which enters into aquatic resources through domestic, industrial and agricultural wastewater. Nitrate ion is an indicator of underground water pollution. In addition to its toxicity, high concentration of this ion in water can cause microbial contamination. High concentration of nitrate in water is notrecognizable through tasting or smelling. The aim of this research was to study the efficiency of nitrate removal in drinking water using zero-valence iron nano-particle (Fe0) and also determination of the optimum conditions. In this study, the ratio of sodium boro-hydride and chloro-ferric (1: 3)w/w was used to prepare zero-valence iron nano-particle. Then, effect of factors such as pH (4, 6, 8, 10), exposure time (5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 and 65 min), concentration of iron nano-particle (10, 15, 30, 45 and 60 g/l) and concentration of nitrate (25, 35, 50, 75, 100, 200, 300, 400 and 500 mg/l) were studied. Absorption level and nitrate reaction dynamics were determined according to the most common isotherms and absorption kinetic. Nitrate removal at pH 4, exposure time of 60 min, 15 g/l of iron nano-particle and initial nitrate concentration of 50 mg/l were recorded as 90%, 99.1, 95 and 70% respectively. Freundlich isotherm (R2=0.988) and Langmuir type 2 (R2=0.978) had the highest correlation to the studied factors. Also, kinetic analysis showed that nitrate absorption by zero-valence iron nano-particlewas done according to grade 2 kinetic (R2=0.989). Findings revealed that nitrate removal level increased as pH decreased and exposure time and concentration of zero-valence iron nano-particle increased. Also, as nitrate concentration increased, removal percentage decreased. Therefore, to remove higher levels of nitrate, optimal experimental conditions should be determined.